With the adoption of the Internet of Things (IoT) and Industry 4.0 features, the device is gradually connected through the industrial communications protocol. In addition, today’s machine-to-machine (M2M) communication protocols are fast becoming one of the standardized options for these protocols. Complicating matters, the IoT communication protocol does not describe a single application layer of communication protocol because there are multiple standards operating simultaneously. Therefore, in addition to the standard Internet communication protocols used in the early IoT, there are now more dedicated IoT communication protocols.
It is not easy to model communication structure and determine communication contracts suitable for specific applications. This article provides an overview of the role of multiple communication protocols and describes the options available for those protocols to make it easier for design engineers to pick the most appropriate integration.
Develop application-level communication protocols for industrial networks
The communication protocol structure between digital M2M and IoT systems can be conceptually divided into different abstraction layers, the most common models being three, four, five or seven layers. These conceptual architectures assume that each layer essentially “hides” detailed work on other devices or algorithms that communicate with it, specifying devices or software layers. This is because these levels are developed to contain only sufficient information to facilitate the exchange of data at hand.
Regardless of the model used, an application layer is established that acts as the highest layer of abstraction between devices that communicate with each other through the network. The application layer can be used as a concept of the Open System Interconnect (OSI) model. This model was developed by the International Organization for Standardization (ISO) for network communications nearly three decades ago. This traditional seven-tier model is a bit too complex to describe some of today’s communication protocols, but it’s still useful to fully understand the data flow in your system.
The physical layer of the protocol transmits the raw data (digital bits) in electrical, radio, or optical signals. This level specifies the pin layout, voltage level alignment, data transfer rate, and line impedance for the physical components that carry the data. Ethernet is a common physical layer communication protocol.
The data chain layer connects network nodes to the appliance to establish a connection and correct errors in the physical layer. In the IEEE 802 standard, the data chain layer is divided into the Media Access Control (MAC) layer (which is also used to connect the device) and the logical link control (LLC) layer, which can be used to identify the next layer (network layer) to be used, and to check for errors and synchronize processing.
Instead, the network layer can transfer packets to network addresses. Internet communication protocol refers to the transmission control communication protocol and the Internet Protocol (TCP/IP) model (explained in the next section of this article), and there is an Internet layer between the data chain and the network layer. In fact, the Internet layer tries to be part of the network layer.
The first of the next three OSI model levels is the transport layer, which ensures communication reliability and security when data sequences are transmitted. The session layer controls when the devices want to connect to each other and when the connections are one-way (single-work) or two-way (duplex). Finally, the performance layer can be transformed to communicate using devices with different syntax.
The focus application layer of this paper is the most advanced level of abstraction, but also the user and the system software interaction layer.
Internet communication protocols in industrial automation
Internet communication protocols are data communication systems, named after each other for passing data between networks (usually mutually) to reach boundaries. Its functionality is typically described in the four-tier model of TCP/IP above. Here, the physical layer or link layer is the same as the physical layer of the OSI model. Conversely, the Internet layer of TCP/IP (roughly a combination of OSI-like data chain and network layer functionality) handles connectivity and data packets. In IPv6, this level uses 128-bit IP addresses to identify hosts on the network and allows more than 1038 unique hosts.
The transport layer of TCP/IP typically consists of a Transport Control Communication Protocol (TCP) or a User Packet Communication Protocol (UDP). TCP is typically used for people interactions, such as e-mail and web browsing. Provides logical wiring, packet transfer notifications, lost packet retransmitting, and process control. However, embedded systems use UDP for lower additional loads and better real-time performance. UDP can be used for domain name servers (DNS), dynamic host setup communication protocols (DHCP), and new IoT applications.
The application layer is the highest level of the TCP/IP network model. Features include features related to the OSI model session and the performance layer.
General TCP/IP application layer communication protocols
Different application layer communication protocols also differ in data bandwidth, real-time capabilities, and hardware requirements. These factors, combined with the familiarity of the plant or OEM team with communication protocols, are often important selection criteria. Early Internet communication protocols, including the Hyper-Text Transmission Communication Protocol (HTTP) and the Simple Mail Transmission Communication Protocol (SMTP), were mostly used for personnel-oriented and personnel-usable communications operations, but the IIoT-oriented TCP/IP communication protocol was more ink-to-machine (M2M) and other industrial communications.
Be aware that using HTTP can be a security concern. This is why any IoT device in such systems is best to have only one client, not the server. This prevents the device from receiving requests that might allow external unauthorized network access to the connection.
Here, the WebSocket communication protocol establishes full duplex communication via HTTP. Otherwise, extended communication protocols (XMPPs) may be preferred for devices that require a large number of devices that take into account good security and instant messaging communications.
If the IoT project is led by someone with IT background, you may prefer to use these familiar standards (from the human readable network). However, newer IIoT communication protocols may be more suitable for M2M and other industrial communications in some cases.
MQTT can be used for vertical connection transmission functions
The most rapidly adopted IIoT is the Information Column Telemetry Transmission (MQTT) communication protocol, which was originally used for IoT devices with limited memory. MQTT operates on a compact processing coverage area with minimal bandwidth, starting with sensors developed by IBM to connect to the tubing. Unlike the Restricted Application Communications Protocol (CoAP), MQTT has been standardized in accordance with ISO/IEC 20922. MQTT uses a more resource-intensive TCP transport layer, which consumes more power, but the message size can be as small as two bytes, or even smaller than the CoAP.
Because of its open nature, MQTT is also particularly easy to implement. No wonder Amazon Web Service’s AWS IoT uses MQTT for messaging (including considerations) and supports MQTT in accordance with v3.1.1 specifications.
MQTT has some limitations over the IoT-specific thin machine-to-machine (LwM2M) communication protocol to be described, possibly because MQTT was originally intended to be used as a telemetry communication protocol. This standard does not include objects, wire monitoring, remote device movements, and so on, so if these characteristics are included, it is usually up to the manufacturer to decide, but how much will degrade the value of standardized communication protocols. MQTT also provides error-free handling. Finally, even if MQTT can improve security with a full TLS communication protocol, this adds additional load.
Primarily used at the enterprise level: AMQP
Advanced Message Column Communication Protocol (AMQP) is another open standard, somewhat similar to MQTT. Provides advanced features such as information queuing. It’s just that amQP has a higher additional burden than MQTT, so it’s not suitable for devices with more limited connections. No wonder this communication protocol is not commonly used in industrial IoT applications, but more often in performance-conscious enterprise communications.
CoAP connected to an improvised unit
The Limited Application Communication Protocol (CoAP) developed by the Internet Engineering Working Group (IETF) allows devices with minimal memory and processing power to communicate with each other in low-power networks. Can be operated at very low additional loads and requirements with a minimum response of only four bytes. CoAP avoids complex transport stacks and instead uses UDP.
CoAP, like HTTP, uses the REST model. The server provides available resources using a URL, while clients can access them through POST, GET, DELETE, and PUT methods. In addition, CoAP can be easily converted to HTTP for integration with other network capabilities, as well as XML and JSON. Engineers can discover that connecting IoT devices with CoAP is very similar to connecting devices using web APIs.
Use the LwM2M to connect the battery-powered unit
One of the application layer communication protocols developed by open Mobile Alliance is LwM2M, specifically designed for IoT applications. Based on CoAP, LwM2M shares properties for smart city applications, containers, truck tracking, automated off-highway routines, and utility monitoring. This standard contains a variety of standard objects that are clearly defined and maintained, as well as connection monitoring and remote device movements. Automated firmware upgrades also simplify the management of the LwM2M wiring unit. While the inclusion of modules such as JSON adds additional load, it also makes it easier for developers to design. Because the LwM2M is specifically designed for IoT applications, it can also be used as a powerful DTLS secure communication protocol without additional load.
DDS is suitable for real-time distributed applications
Data Distributed Services (DDS) are somewhat different and are often classified as M2M mediation software rather than application layer communication protocols. Provides safe and high-performance connectivity in applications such as self-driving cars, power generation, and air traffic control systems. In these applications, DDS enables embedded system connectivity for distributed control so as not to become overly dependent on the gateway. DDS can also handle the routing and delivery of messages without the intervention of the application. In addition, the quality of DDS service parameters can be set, so network operations can be optimized to meet the needs of the job, subject to system constraints.
Conclusion: IIoT application layer communication protocol
Any communication protocol has its advantages and disadvantages, but open source options can be deployed quickly and have the security that best suits IoT applications (so they prefer to use due to low additional load). The increasing computing power of embedded systems and system single-chip (SoC) devices continues to facilitate the implementation of IIoT and further expand the potential applications of various communication protocol application layers.